Portable devices are becoming more ubiquitous in everyday life. They influence how we communicate with each other, interact with our music, and organize our lives. For example, many consumers enjoy their music on portable audio players, such as MP3 players or cellular phones. Portable devices become easier and more enjoyable to use when they shrink in size while offering the same capabilities. The desire for smaller electronic devices creates a tension between requirements of small size and maintaining loud and bass-rich sound, whether from an internal micro-speaker or connected external speakers (such as headphones). Dimensions of loudspeakers in portable devices are often limited by the form factor and layout of the device itself. Furthermore, the introduction of smart accessories and modular cellular phone design has expanded the variety of speaker designs available for use with a portable electronic device. One such speaker design is a ported rear enclosure which can provide for enhanced bass.
FIGS. 1A and 1B illustrate an example of the design difference between a sealed speaker and a ported speaker. A sealed speaker, as illustrated in FIG. 1A, may include a sealed enclosure 106 around a back cavity of the speaker and a transducer 102. A ported speaker, as illustrated in FIG. 1B, may include a ported enclosure 108 around a back cavity of the speaker along with a transducer 102 and a port 104 in the enclosure. The port 104 allows air to be exchanged between the inside of the enclosure 108 and the surrounding space as illustrated in FIGS. 2A-B. In FIG. 2A, air is forced out of the enclosure 108 through port 104 as the cone moves inwards. In FIG. 2B, air is drawn into the enclosure 108 through port 104 as the cone moves outward. Thus, air may move in and out of the enclosure in accordance with movement of the cone 110 during operation of the speaker.
FIG. 3 illustrates one of the potential advantages of a ported speaker in which the bass sound pressure level (SPL) frequency response of the speaker can be extended by the addition of a properly tuned port. A line 302 illustrates frequency response for low frequencies for a ported speaker, such as that of FIG. 1B; and a line 304 illustrates frequency response for low frequencies for a sealed speaker, such as that of FIG. 1A. A resonance frequency of the port 104 creates constructive interference between the port 104 and the cone 110, such as shown below 100 Hertz in line 302, thus extending the bass frequency response of the speaker. Below the resonance frequency, the interference will be destructive, thus creating the sharp drop off, such as shown below 30 Hertz in line 302. The port 104 allows for increased bass frequency response for the same power consumption as a sealed speaker.
However, the availability of varied enclosure types has introduced design challenges. For example, the tuning or performance of speakers can be highly dependent upon the port configuration. Speaker protection may be necessary to maintain operation of the speaker within excursion and thermal limits, for example, when a boosted amplifier is used to maximize volume through overdriving the speaker. Thus, design of speakers with ported and sealed enclosures can necessitate specific tuning algorithms tailored to the specific speaker design to protect the speaker as well as to maintain high audio quality. Furthermore, the speaker sealing may change during operation of the device. For example, ports of ported speakers may become blocked during operation, such as in mobile devices where a user can unknowingly place his hand over a port causing a speaker response to appear like a sealed speaker rather than a ported speaker. Sealed speakers may develop leaks over time, causing the speaker to behave like a ported speaker rather than a sealed speaker. Thus, a fixed tuning algorithm for a speaker may be inadequate to maintain high audio quality and to protect the speaker.
Shortcomings mentioned here are only representative and are included simply to highlight that a need exists for improved electrical components, particularly for audio systems employed in consumer-level devices, such as mobile phones. Embodiments described herein address certain shortcomings but not necessarily each and every one described here or known in the art. Furthermore, embodiments described herein may present other benefits than, and be used in other applications than, those of the shortcomings described above.